Group items tagged

"...scientists in Germany have built a device that can effectively make objects invisible to sound waves. The performance of the acoustic "invisibility cloak" exceeds that of existing electromagnetic devices and could open up new ways of manipulating waves, including the development of shields against seismic waves."

shit.... they are a few months ahead of us it seems ... :-( what is the impact on our ariadna??

Researchers in the US have made a "carpet cloak" that makes objects invisible to sound waves. The device is the first such cloak to work in air and could be used to improve the acoustics in concert halls or even to control unwanted noise.

and more invisibility ... have a look at this José! ...

Cheap and scalable invisibility cloaks being developed. The setup is so trivial that I would almost call it a "trick" (as in "Magicians trick"): 6 prisms of n=1.78 glass. Nontheless, it does the job of cloaking an object at visible wavelengths and from several directions.

Is this really new? I don't know, but I know that the original idea of cloaking was pretty different. When cloaking as an application of transformation optics became popular people tried to make devices that work for any incidence angle, any polarization and in full wave optics (not just ray approximation). This is really hard to achieve and I guess that the people that tried to make such devices knew exactly that the task becomes almost trivial by dropping at least two of the three conditions above.

I think it is very easy to call something trivial when you're not the one who invested considerable time (5 min in my case) to design a cloaking device and fill the coffee mugs with water... Also, I did not really violate that many conditions: true I reduced the number of dimensions in which the device works to 1 (as opposed to the 2 dimensions of many metamaterial cloaks). However the polarization should not be affected in my setup as well as the wave phase and wave vector (so it works in full wave optics) - apart maybe from the imperfect lens distortion, but hey I was improvising.

and all this without magic metamaterials ...

It's funny to see how people get more and more humble in the desperate attempt to save their stupid ideas... At the beginning was the brave and bold aim to cloak something in free space (in a sphere or a cylinder). This requires inhomogeneous, anisotropic, magnetic materials; hopeless!! So one reduces to one polarization, now we have inhomogenous, anisotropic materials; still hopeless! At this point one downgraded the pretension: instead of cloaking in free space, we make a "carpet cloak" and hide an object behind an invisible dent in a mirror. But if that shall be continuous, we still need inhomogeneity and this is very hard. So now instead of a dent we take a cone and then it is claimed to work ... for ONE polarization. But of course the cloak can't work at all incident angles... irony of fate: everything is now made from birefringent media, the antithesis of what the metamaterials dogma was at the beginning!

Hi Luzi, can you please send me the paper. We are writing a project based on sulfates and carbonates, and all this BS sounds great for the introduction (The authors used Calcite as birefringent material)

Electromagnetic analysis of cylindrical invisibility cloaks and the mirage effect

"Applications for the film extend beyond getting rid of wrinkles, though. It can safely deliver medications for 24 hours at a time as well as protect the user's skin, particularly over wounds. Additionally, the XLP material can reduce moisture loss. "

now active cloaking ... Luzi?, Sante?, Anna?

Here is a first entry for our canweuseitforspace database. Jose, apparently this invisibility cloack is not that difficult after all!!!! Watch the youtube video.....

To keep you updated in the field of metamaterials. "Invisible sensors" are a hot topic at the moment. Of course, mainly due to military applications. Might be interesting to sense something while minimizing the perturbations due to the sensor.

And all seems to be allowed by transformation optics ..... mah

We don't have Science Express subscription here, so I have to wait till the normal paper is out. From what I heard about it, I doubt that this would have made it to Science without the names Pendry and Wegener in the autor list! Certainly, they are two of the smartest guys in Metamaterials, but they are also two of the absolut class A sellers. Pendry by definition is the first in whatever (at least in HIS talks...) but apart from this he's a very nice guy. Better let's not try to characterize Wegener...

large invisible cables and self-cleaning releasable superadhesive materials

Be careful, the article is written by the company who did the migration to Ubuntu. Here is a comment by a police guy from IT (in french...). In brief he says that tyhe migration was not a problem for most of the people; exepc for some probleme with access. But it did cost money ! and the saving was not the main argument. "Personnellement concerné par la news qui n'en est pas une, je peux vous assurer que le message de Canonical est surtout commercial... Le choix d'Ubuntu est dû à son hégémonie et le fait que ce soit basé sur du Debian qui est considéré comme très stable. La distrib est d'une maintenance plus aisée que la plupart de celles qui ont été testées. "4500 postes" veut dire "4500 unités de gendarmerie" donc dans les brigades que vous connaissez... Pour ce qui est d'OpenOffice, le passage s'est fait assez tranquillement sauf pour les applis Access qui ont eu un peu de mal à passer sur le module Base...La plupart ont été reprise au sein d'applis php/mysql ou d'applis centralisées... Aujourd'hui, les gendarmes qui je le rappelle ne sont pas informaticiens mais vivent pour vous (au sens le plus strict je vous l'assure) utilisent donc firefox/thunderbird et oppenoffice en clients lourds, le reste étant des applis sur l'intranet ou "invisibles" pour l'utilisateur. Le passage à Ubuntu ne gène en rien dans l'utilisation car le trio précédemment cité est déjà connu et maîtrisé par nombre de mes collègues. Je ne suis pas censé m'exprimer en lieu et place de mes supérieurs mais à titre personnel, le choix d'Ubuntu est un choix intelligent car c'est une distribution avec une prise en main très accessible et avec une maintenance vraiment aisée pour les spécialistes informatiques dont je fais partie...Il ne faut pas oublier qu'une distribution plus élitiste aurait été maîtrisée par moins de monde et donc la maintenance aurait été plus coûteuse... Donc aujourd'hui nous "maîtrisons" cette part de notre infrastructure et la trans

Lotus Notes doesn't run on Linux anyway...

I think Lucas didn't know he would have such an impact in science with Star Wars...!

do you think it could be the dark side of The Force?

what else...?

I forwarded the link to my experimental colleagues and here is the comment from Sergei (the master himself:) "this is what Igor has been doing - an array of plasmonic nanocables. This basically works as a wire-medium slab. All their epsilon and mu are rubbish." * If Sergei is as strict as in this comment, then it IS rubbish. He's not one of the notorious complainer (as e.g. myself.) * Please DO NOT FORWARD this to anybody else, Sergei's comment is NOT FOR PUBLIC USE!

UPDATE: I had a short chat with Sergei and Pekka, Sergei noticed that there is an increasing number of papers on metamaterials, especially in Nature and Science, which are simply wrong, this one being an example. * The idea is based on a very well known effect of wired media. What appears to be interesting about this paper is that they manage to make an optical analogue with aparently low losses. This could be interesting. * The whole interpretation as NIM, "wrong" refraction etc. is total nonsense.

wow, good to know ! But for the privacy you should be aware that this is a public group, so anyone has access to our comments i think !

more transformation optics ... 

I still believe that it is worth to check the thermal, mechanical and chemical properties of the developed metamaterials. For hyperbolic re-entries the radiation is still the dominating heat load source and a dominating bandwith may be indentified. A resistive metamaterial should be placed on the nose cap of the entry body in order to reduce local radiation heat load.